Adjustable occipital plate

ABSTRACT

An occipital plate for use in an occipito-cervico-thoracic (OCT) construct is mounted to a patient&#39;s occipital bone. The occipital plate includes an elongate central section aligned with a midline of the base and a pair of angled sections that project away from the central section and include attachment assemblies for securing a rod to the occipital plate. The attachment assemblies have multi-adjustability features. At least a portion of the attachment assemblies is rotatable with respect to the base so that the rods may be coupled to the occipital plate at a variety of angles with respect to the midline. The angular adjustability may accommodate any misalignments in the rods. Additionally, the position of the attachment assemblies relative to the midline of the occipital plate is adjustable to thereby provide for medial-lateral adjustability when attaching the rods to the occipital plate as part of the OCT construct.

FIELD OF THE INVENTION

This invention relates generally to fixation devices used in orthopedicsurgery. The invention relates more particularly to devices used forcervical posterior fixation utilizing a plate attached to a bone in theoccipital region and secured to a rod which attaches to a cable, wire,plate, or screw fastened in the spinal region.

BACKGROUND OF THE INVENTION

Fixation devices are used in orthopedic surgery to stabilize bones suchas those in the spinal column. One type of fixation device includes aplate attachable to a portion of a bone. The plate may be connected toanother bone or another portion of the same bone, directly or throughother connecting devices. For example, posterior fixation devices caninclude a plate fastened to the skull, or occiput, one or more rodsrunning longitudinally along the spine and connected to the plate, andvertebral mounts such as plates, cables, wires, hooks, screws, or otherconnectors attached to a vertebra and connected to the rod.

A number of such mechanisms are known in the art. To accommodate thevariation in patient size and anatomy, a plate often needs to be chosenfrom a set of plates of multiple sizes and/or varying geometry. Thisresults in a higher cost of the assembly and a need to maintain separateinventory of the various size and geometry occiput plates. It alsoincreases the surgical time because the surgeon must search for thedevice that best fits the patient. Moreover, in conventional mechanisms,to connect the rod or rods with the plate requires that the rods beprecisely aligned with the connection features on the plate.Misalignment of the rods with the plates results in the surgeon makingad hoc adjustments to the device, which further increases the surgicaltime. Accordingly, there is a need for an improved fixation plate thatreduces inventory and surgery duration while still providing a secure,reliable and robust connection between the rods and the occipital orother bone structure.

SUMMARY OF THE INVENTION

This invention addresses these and other shortcomings in the prior art.In one embodiment, the invention is directed to a fixation system forconnecting a stabilizing system to a bone. More specifically, theinvention in one embodiment is directed to an occipital plate for use inan occipito-cervico-thoracic (OCT) construct in which an occipital plateis mounted to a patient's occipital bone. Typically, a pair of rods isreleasably secured in spaced relation to each other to the occipitalplate and a number of vertebral mounts which may include plates, cables,wires, hooks, screws, or other connectors that secure the rods relativeto specific vertebrae.

In one embodiment, the occipital plate includes a base with an elongatecentral section oriented with a midline of the base. A pair of angledsections extends from the central section on opposite sides of themidline and forms an angle with respect to the midline. The angledsections include attachment assemblies for securing one of the rods tothe occipital plate. The attachment assemblies have multi-adjustabilityfeatures. To this end, at least a portion of the attachment assembliesis rotatable with respect to the base so that the rods may be coupled tothe occipital plate at a variety of angles with respect to the midline.In this way, the adjustability of the attachment assemblies mayaccommodate any misalignments in the rods. Additionally, the position ofthe attachment assemblies relative to the midline of the occipital plateis adjustable to thereby provide for medial-lateral adjustability whenattaching the rods to the occipital plate as part of the OCT construct.

In specific embodiments, the attachment assemblies include a slidemember which mates with the angled section of the occipital plate in adove-tail joint configuration and a post extending from the slide memberthat receives a rod therein. A set screw is threadably coupled to thepost to secure the rod relative to the attachment assembly and thereforeto the occipital plate. The attachment assemblies may include an anglelimiting mechanism that limits the range of angles through which therotatable portion of the attachment assemblies may rotate relative tothe occipital plate.

Therefore, as a result of this invention, a single occipital plate maybe utilized for a variety of patient sizes and configurations andprovides efficient and secure multi-adjustability, i.e., both angularadjustability and adjustability in a medial-lateral direction, whenattaching the rods as part of an OCT construct.

These and other objects, advantages and features of the invention willbecome more readily apparent to those of ordinary skill in the art uponreview of the following detailed description taken in conjunction withthe accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of this specification, illustrate embodiments of the invention and,together with a general description of the invention given above, andthe detailed description given below, serve to explain the invention.

FIG. 1 is a posterior view of an exemplary occipito-cervico-thoracicconstruct utilizing an adjustable occipital plate according to oneembodiment of the invention;

FIG. 2 is an exploded plan view of the components of one embodiment ofthe occipital plate according to this invention;

FIG. 3 is a cross-sectional view of the occipital plate shown in FIG. 2generally taken along line 3-3;

FIG. 4 is a cross-sectional view of the occipital plate shown in FIG. 2generally taken along line 4-4;

FIG. 5 is a partial exploded plan view of the occipital plate shown inFIG. 1 illustrating the adjustability of the attachment assembly shownin FIG. 1;

FIG. 6 is a perspective view of an attachment assembly according toanother embodiment of the invention;

FIG. 7 is a partial exploded plan view of an occipital plateillustrating the adjustability of the attachment assembly shown in FIG.6;

FIG. 8 is a perspective view of an attachment assembly according toanother embodiment of the invention;

FIG. 9 is a plan view of the attachment assembly shown in FIG. 8;

FIG. 10 is a partial exploded plan view of an occipital plateillustrating the adjustability of the attachment assembly shown in FIG.8;

FIG. 11 is a perspective view of an attachment assembly according toanother embodiment of the invention;

FIG. 12 is a plan view of the attachment assembly shown in FIG. 11; and

FIG. 13 is a partial exploded plan view of an occipital plateillustrating the adjustability of the attachment assembly shown in FIG.11.

DETAILED DESCRIPTION

Referring to FIG. 1, one embodiment of an adjustable occipital plate 10according to this invention is shown utilized as part of anoccipito-cervico-thoracic (OCT) construct 12. The adjustable occipitalplate 10 in FIG. 1 is mounted to the occipital bone 14 of a patient 16.One or more rods 18 are attached to the occipital plate 10 and runsubstantially along the spine 20 of the patient 16 and are attached tovarious segments of the spine 20 such as selected vertebrae 22 byvertebral mounts 24 according to any one of a know variety of suchdevices.

As shown in FIG. 2, the occipital plate 10 according to this embodimentof the invention includes a base plate 26 having an elongate centralsection 28 with a midline 30, which is generally aligned with the spine20 when mounted to the occipital bone 14. The central section 28 mayinclude a number of holes or apertures 32, three of which are shown, forbone screws 34 to mount the occipital plate 10 to the occipital bone 14or another portion of the patient 16. The occipital plate 10 isgenerally symmetric relative to the midline 30 and includes a pair ofangled sections 36 that at least have a component that projectslaterally outward in opposite directions from the midline 30, i.e., in adirection that is at least in part perpendicular to the midline 30. Inparticular, the angled sections 36 form an angle A with respect to themidline 30. The angle A may be selected based on the specificapplication, but is generally between approximately 10° andapproximately 90°, and more particularly between approximately 30° andapproximately 70°. The invention, however, is not so limited as theangled sections 36 may be angled with respect to the midline 30 by anamount that provides a sufficient amount of lateral travel forconnecting to rods 18 as is explained in more detail below. Each angledsection 36 may include a hole or aperture 38 to receive a bone screw 34there through for an additional mounting location to the occipital bone14 or other bone.

As shown generally in FIG. 1 and more specifically in FIG. 2, theoccipital plate 10 in accordance to one embodiment of this inventionincludes an elongate slot 40 formed in each of the angled sections 36which extends substantially parallel to a length of its respectiveangled section 36. An attachment assembly, generally shown at 42, ismounted within the slot 40 and is capable of movement along the slot 40.Movement of the attachment assemblies 42 along slots 40 providesmedial/lateral adjustability (i.e., in a direction substantiallyperpendicular to midline 30) of the attachment assembly 42 relative tothe midline 30 of the central section 28 of the occipital plate 10 toallow for selective positioning of the rods 18 attached to the occipitalplate 10 by the attachment assemblies 42. Depending on the angle A,movement of the attachment assemblies 42 along slots 40 may also providea cephlad/caudal adjustability (i.e., in a direction substantiallyparallel to midline 30) of the attachment assemblies 42 that may beadvantageous in some applications.

In one embodiment, each rod attachment assembly 42 includes arectangular-shaped slide member 44 having an upper wall 46, a lower wall48, and a pair of spaced apart sidewalls 50 projecting generallyperpendicularly from the lower wall 48. Each of the sidewalls 50includes an extension 52 projecting outwardly or away from the opposingsidewall 50. The spaced side edges of the slot 40 in each of the angledsections 36 of the base plate 26 each includes a rectangular-shapedgroove 54 adapted to mate with one of the extensions 52 projecting fromthe sidewall 50 of the slide member 44, thereby forming a dove-tailjoint construct between the attachment assembly 42 and the base plate26. This dove-tail type of construction allows movement of the slidemember 44 along slot 40 but limits movement of the slide member 44 in adirection substantially perpendicular to the slot 40. Thus, the slidemember 44 is constrained to move along slot 40. The slide member 44 maybe positioned in slot 40 in ways generally known in the art. Forexample, the terminating ends of angled sections 36 may be configured asend caps that allow the slide member 44 to be positioned in the slot 40and which may subsequently be secured to the angled sections 36, such asby welding or other securing techniques, to retain the slide member 44in the slot 40. Alternatively, the slide members 44 may be configured toelastically deform so as to allow the slide member 44 to be positionedin the slot 40. Once positioned in the slot 40, however, the slidemember 44 returns to its non-deformed state and operates as describedabove.

In an exemplary embodiment, each slide member 44 includes a post 56extending upwardly from the upper wall 46. Each post 56 includes acavity 58 extending through the post 56 having a pair of spaced apart,generally straight sidewalls 60 and an arcuate lower wall 62. The cavity58 further includes an opening 64 at an end opposite the arcuate lowerwall 62 for receiving a rod 18 of the OCT construct 12. In thisembodiment, the post 56 is not rigidly coupled to slide member 44, butinstead is coupled so as to allow rotation of post 56 relative to slidemember 44 about an axis 66 (FIGS. 3-4). For example, post 56 may becoupled to slide member 44 by a rivet 68. The invention, however, is notso limited as those of ordinary skill in the art will recognize otherconnectors that may be used to provide rotation of the post 56 relativeto the slide member 44. The ability to rotate the posts 56 allows thesurgeon to adjust the attachment assembly 42 so as to align the cavity58 with the rods 18. In this way, any misalignment of the rods 18 may becompensated for through the rotation of the posts 56 thereby providing amore robust attachment between the rods 18 and the base plate 26 withoutsignificant time-consuming adjustments made by the surgeon.

The rod 18 is clamped to the attachment assembly 42, and as a result theoccipital plate 10, by a set screw 70. The set screw 70 includes athreaded shaft 72 that is received in a threaded upper portion 74 ofpost 56. A head 76 of the set screw 70 sits atop the post 56. The head76 of the set screw 70 includes a hex-shaped socket 78 to receive awrench or other driver (not shown) to adjust the set screw 70 relativeto the arcuate lower wall 62. The distal end of the shaft 72 of setscrew 70 is juxtaposed against the upper side of rod 18 to secure therod 18 to the attachment assembly 42. As such, the surgeon is able tosecure the rod 18 relative to the midline 30 of the base plate 26 bysetting the set screw 70.

Therefore, the occipital plate 10 according to one embodiment of theinvention provides for medial-lateral adjustability when attaching therods 18 as part of an OCT construct 12. The occipital plate 10 alsoprovides angular adjustability by permitting rotation of at least aportion of the attachment assembly 42 so as to accommodate anymisalignment of the rods 18 with the attachment assembly 42. The surgeononly needs to tighten one set screw 70 for each attachment assembly 42to lock the rod 18 relative to the midline 30 of the occipital plate 10.The adjustability of the attachment assembly 42 is illustrated in FIG.5. For instance, the attachment assembly 42 is shown in one position(solid line) spaced a first distance from the midline 30 and adapted toreceive a rod 18 in a first angular orientation. For illustrativepurposes, the attachment assembly 42 is also shown in another position(phantom lines) spaced a second distance from the midline 30 and adaptedto receive a rod 18 in a second angular orientation. The ability toadjust the medial-lateral distance from the midline 30 is a result ofthe slide member 44 moving along slot 40 in angled sections 36, and theability to adjust to the angular orientation of the rod 18 is a resultof the post 56 rotating relative to the slide member 44 so that thecavity 58 aligns with the rod 18. Such a multi-adjustability featureimproves the use and functionality of attachment assembly 42 for OCTconstruct 12.

Other attachment assemblies and mechanisms can be utilized for securingthe position of the rods 18 relative to the midline 30 of the occipitalplate 10. For instance, FIGS. 6 and 7, in which like reference numeralsrefer to like features in FIGS. 1-5, illustrate an alternate attachmentassembly in accordance with an embodiment of this invention. Inparticular, these figures show an attachment assembly 80 having a slidemember 82 rigidly coupled to a post 84 extending from an upper surfaceof the slide member 82. The slide member 82 and post 84 may beintegrally formed with each other or may be separate components that arerigidly affixed to each other through a subsequent assembly operation,such as by gluing, welding, and other processes known to those ofordinary skill in the art. Alternatively, the post 84 may rotaterelative to slide member as described above.

The slide member 82 and post 84 each have a circular cross-sectionalshape with the diameter of the post 84 being less than the diameter ofthe slide member 82 to define an annular flange 86 along the peripheryof the slide member 82. In a manner similar to that shown in FIG. 3, thespaced side edges of each of the slots 40 in the angled sections 36 ofbase plate 26 each include a rectangular-shaped groove 54 (FIG. 3)adapted to mate with the annular flange 86 of the slide member 82. Thistype of construction allows movement of the slide member 82 along slot40 but limits movement of the slide member 82 in a directionsubstantially perpendicular to the slot 40. Thus, the slide member 82 isconstrained to move along slot 40. Moreover, due to the circulargeometry of the slide member 82, the attachment assembly 80 is able torotate within the slot 40 and relative to the base plate 26. Forinstance, when in the slot 40, the attachment assembly 80 can rotaterelative to axis 66.

As in the previous embodiment, the post 84 includes a cavity 58 adaptedto receive a rod 18, and further includes threaded upper portion 74adapted to receive set screw 70 to clamp the rod 18 to the attachmentassembly 80. The operation of attachment assembly 80 is similar to thatdescribed previously. An occipital plate 88 having an attachmentassembly 80 also provides for medial-lateral adjustability whenattaching the rods 18 as part of an OCT construct 12. The occipitalplate 88 also provides angular adjustability by permitting rotation ofthe attachment assembly 80 so as to accommodate any misalignment of therods 18 with the attachment assembly 80. Again, the surgeon only needsto tighten one set screw 70 for each attachment assembly 80 to lock therod 18 relative to the midline 30 of the occipital plate 88.

The adjustability of the attachment assembly 80 is illustrated in FIG.7. The attachment assembly 80 is shown in one position (solid lines)spaced a first distance from the midline 30 and adapted to receive a rod18 in a first angular orientation. For illustrative purposes, theattachment assembly 80 is also shown in another position (phantom lines)spaced a second distance from the midline 30 and adapted to receive arod 18 in a second angular orientation. The ability to adjust themedial-lateral distance from the midline 30 is a result of the slidemember 82 moving along slot 40 in angled sections 36, and the ability toadjust to the angular orientation of the rod 18 is a result of theattachment assembly 80 rotating relative to the base plate 26 so thatthe cavity 58 aligns with the rod 18. Thus, attachment assembly 80 alsoprovides a multi-adjustability feature that improves the use andfunctionality of attachment assembly 80 for OCT construct 12.

FIGS. 8-10, in which like reference numerals refer to like features inFIGS. 1-7, show yet another embodiment of an attachment assembly inaccordance with an embodiment of this invention. In this embodiment,however, the range over which the attachment assembly or a portionthereof, may be rotated is limited. For instance, the embodiments shownand described in FIGS. 1-7 provide full rotation of the rotatableportion of the attachment assembly, i.e., the rotatable portion mayrotate a full 360° within slot 40 In some applications, however, it maybe desirable to limit the full range of rotation of the attachmentassembly. Limiting the range of rotation may facilitate insertion of therods 18 into their respective cavities in the attachment assemblies. Forinstance, depending on the range of rotation permitted, the attachmentassemblies may operate so as to essentially self align with the rods asthe rods are inserted into their respective cavities.

The embodiment of the attachment assembly 90 is similar in constructionto the attachment assembly 80 shown in FIGS. 6 and 7 and describedabove. However, the attachment assembly 90 includes an angle limitingmechanism that limits the range of angles through which the rotatableportion of the attachment assemblies rotates. In one embodiment, theangle limiting mechanism includes a pair of opposed triangularly-shapedwing members 92 projecting from the periphery of the slide member 82 soas to define a pair of bearing surfaces 94 for each of the wing members92. The cross dimension between the apexes of the wing members 92 isgreater than the width of the slot 40 along opposed grooves 54 in angledsections 36 (FIG. 3). The bearing surfaces 94 are angled with respect toan axis 95 (FIG. 9) by an angle B, which may control the amount ofrotation of the attachment assembly 90 about the axis 66 when attachmentassembly 90 is in slot 40. The rotation of the attachment assembly 90 islimited because a bearing surface 94 of opposed wing members 92 engagesthe wall of grooves 54 in slot 40. When the bearing surfaces 94 engagethe grooves 54, further rotation in that particular direction (e.g.,clockwise or counterclockwise) is prevented. By way of example, for anangle B of approximately 30°, the attachment assembly 90 may rotateabout axis 66 for 30° in a clockwise direction, and 30° in acounterclockwise direction when the wing members 92 initially pointalong a direction generally parallel to the slot 40, as shown in solidin FIG. 10. The angle B may be between approximately 10° andapproximately 40°, and more preferably approximately 30°. The invention,however, is not so limited as those of ordinary skill in the art mayconfigure the wing members 92 to limit rotation of the attachmentassembly 90 to a desired range.

As in the previous embodiment, the post 84 includes a cavity 58 adaptedto receive a rod 18, and further includes threaded upper portion 74adapted to receive set screw 70 to clamp the rod 18 to the attachmentassembly 90. The operation of attachment assembly 90 is similar to thatdescribed previously. An occipital plate 96 having an attachmentassembly 90 also provides for medial-lateral adjustability whenattaching the rods 18 as part of an OCT construct 12. The occipitalplate 96 also provides angular adjustability by permitting rotation ofthe attachment assembly 90 so as to accommodate any misalignment of therods 18 with the attachment assembly 90. Unlike the previousembodiments, however, the rotation of attachment assembly 90 has alimited range due to the wing members 92 and their engagement with thegrooves 54 in slots 40. Such a configuration may facilitate insertion ofthe rods 18 into the cavities 58 in posts 56. Again, the surgeon onlyneeds to tighten one set screw 70 for each attachment assembly 90 tolock the rod 18 relative to the midline 30 of the occipital plate 96.

The adjustability of the attachment assembly 90 is illustrated in FIG.10. The attachment assembly 90 is shown in one position (solid line)spaced a first distance from the midline 30 and adapted to receive a rod18 in a first angular orientation. For illustrative purposes, theattachment assembly 90 is also shown in another position (phantom lines)spaced a second distance from the midline 30 and adapted to receive arod 18 in a second angular orientation. The ability to adjust themedial-lateral distance from the midline 30 is a result of the slidemember 82 moving along slot 40 in angled sections 36, and the ability toadjust to the angular orientation of the rod 18 is a result of theattachment assembly 90 rotating relative to the base plate 26 so thatthe cavity 58 aligns with the rod 18. Thus, attachment assembly 90 alsoprovides a multi-adjustability feature that improves the use andfunctionality of attachment assembly 90 for OCT constructs 12.

In one aspect of the invention, as shown in FIG. 9, an axis 97 throughcavity 58 in post 56 may be rotationally offset from axis 95 extendingthrough the wing members 92 by an angle C. In one embodiment, the offsetangle C is substantially equal to angle A. In this case, when theattachment assembly 90 is in slot 40 and axis 95 is substantiallyparallel to the slot 40, the axis 97 is substantially parallel tomidline 30, and may receive a rod 18 that likewise is substantiallyparallel to midline 30. Such a configuration is shown in solid in FIG.10. As explained above, the rods 18 may be misaligned so that theattachment assembly 90 must be rotated to align the cavity 58 with rod18. Of course, the rods 18 may be misaligned such that either aclockwise rotation or a counterclockwise rotation is required to alignthe cavity 58 with the rod 18. To provide increased flexibility inaccommodating misaligned rods, axis 97 should be parallel to midline 30when axis 95 is parallel to the slot 40 to define a neutral angularposition. In the neutral angular position, the attachment assembly 90may rotate by approximately an equal amount in either the clockwise orcounterclockwise direction, that amount being controlled by the angle Bas previously discussed. By configuring the wing members 92 and cavity58 in the manner dictated by the neutral angular position, theattachment assembly 90 is capable of accommodating misalignments of therods by approximately an equal amount in either direction.

FIGS. 11-13, in which like reference numerals refer to like features inFIGS. 1-10, show yet another embodiment of an attachment assembly inaccordance with an embodiment of this invention. In this embodiment, therange over which the attachment assembly may be rotated is againlimited. As noted above, the limited range of rotation may facilitateinsertion of the rods into the attachment assemblies and, depending onthe range of rotation permitted, the attachment assemblies may operateso as to essentially self align with the rods as the rods are insertedinto their respective cavities.

The embodiment of the attachment assembly 98 includes a slide member 100rigidly coupled to a post 102 extending therefrom. As noted above, theslide member 100 and the post 102 may be integrally formed with eachother or may be separate components that are rigidly affixed to eachother. The slide member 100 is generally oblong having a first crossdimension 104 and a second cross dimension 106 that is less than thefirst cross dimension 104. In this embodiment the angle limitingmechanism is not associated with the slide member 100, but is insteadassociated with the post 102. Thus, material that would otherwise beused to form the slide member 100 may be removed (see phantom in FIG.12). Such a design may reduce material costs and may provide additionaladvantages. The post 102 is also generally oblong in a direction 90°offset from that of the slide member 100. The post 102 has a first crossdimension 108 that is less than the first cross dimension 104 of theslide member 100 and a second cross dimension 110 that is approximatelyequal to the second cross dimension 106 of the slide member 100. Such aconfiguration defines a pair of opposed flanges 112. In a manner similarto that shown in FIG. 3, the spaced side edges of each of the slots 40in the angled sections 36 of base plate 26 each include arectangular-shaped groove 54 adapted to mate with one of the flanges 112of slide member 100. The attachment assembly 98 may be positioned withinslot 40 in a manner previously described. This type of constructionallows movement of the slide member 100 along slot 40 but limitsmovement of the slide member 100 in a direction substantiallyperpendicular to the slot 40. Thus, the slide member 100 is constrainedto move along slot 40. In addition, due to the geometry of the slidemember 100, the slide member 100 is capable of rotating within slot 40and relative to base plate 26 about axis 66. As discussed below,however, the rotation of the attachment assembly 98 is limited due tothe interaction of the post 102 with the slot 40.

As shown in FIG. 13, the slot 40 in angled section 36 has an opening 114with a cross dimension 116 that is greater than the first crossdimension 108 of the post 102 but is less than the second crossdimension 110 of the post 102. Thus, the post 102 fits within slot 40when the long dimension of the post 102 (i.e., second cross dimension110) is generally parallel with the slot 40, but does not fit within theslot 40 as the attachment assembly 98 is rotated. To this end, the outersurface 118 of the post 102 includes bearing surfaces 120 adapted tocontact an inner edge 122 of opening 114 to limit the rotation of theattachment assembly 98 in both a clockwise and counterclockwisedirection. Those of ordinary skill in the art will recognize how to varyor adjust the cross dimensions 108, 110 of the post 102 so as to achievea desired range of rotation of the attachment assembly 98 relative tothe base plate 26 when the attachment assembly 98 is in slot 40.

As in the previous embodiments, the post 102 includes a cavity 58adapted to receive a rod 18, and further includes threaded upper portion74 adapted to receive set screw 70 to clamp the rod 18 to the attachmentassembly 98. The operation of attachment assembly 98 is similar to thatdescribed previously. An occipital plate 124 having an attachmentassembly 98 also provides for medial-lateral adjustability whenattaching the rods 18 as part of an OCT construct 12. The occipitalplate 124 also provides angular adjustability by permitting rotation ofthe attachment assembly 98 so as to accommodate any misalignment of therods 18 with the attachment assembly 98. Like the embodiment shown inFIGS. 8-10, the rotation of attachment assembly 98 has a limited rangedue to sizing of the post 102 and the engagement of the bearing surfaces120 with the inner edges 122 in slot 40. Such a limited rotationconfiguration may facilitate insertion of the rods into the cavities 58.Again, the surgeon only needs to tighten one set screw 70 for eachattachment assembly 98 to lock the rod 18 relative to the midline 30 ofthe occipital plate 124.

The adjustability of the attachment assembly 98 is illustrated in FIG.13. The attachment assembly 98 is shown in one position (solid lines)spaced a first distance from the midline 30 and adapted to receive a rod18 in a first angular orientation. For illustrative purposes, theattachment assembly 98 is also shown in another position (phantom lines)spaced a second distance from the midline 30 and adapted to receive arod 18 in a second angular orientation. The ability to adjust themedial-lateral distance from the midline 30 is a result of theattachment assembly 98 moving along slot 40 in angled sections 36, andthe ability to adjust to the angular orientation of the rod 18 is aresult of the attachment assembly 98 rotating relative to the base plate26 so that the cavity 58 aligns with the rod 18. Thus, attachmentassembly 98 also provides a multi-adjustability feature that improvesthe use and functionality of attachment assembly 98 for OCT construct12. In addition, the oblong configuration of slide member 100 alsoprovides for a more efficient use of the length of slot 40. In otherwords, the attachment assembly 98 has an increased length of travelalong slot 40 as compared to other designs due to the removal ofmaterial along the second cross dimension 106 of the slide member 100.

As shown in FIG. 12, an axis 124 through cavity 58 in post 56 may berotationally offset from an axis 126 generally parallel to the long orsecond dimension of post 102 by an angle C. In one embodiment, theoffset angle C is substantially equal to angle A. In this case, when theattachment assembly 98 is in slot 40 and axis 126 is substantiallyparallel to the slot 40, the axis 124 is substantially parallel tomidline 30, and may receive a rod 18 that likewise is substantiallyparallel to midline 30. As explained above, the rods 18 may bemisaligned so that the attachment assembly 98 must be rotated to alignthe cavity 58 with rod 18. Of course, the rods 18 may be misaligned suchthat either a clockwise rotation or a counterclockwise rotation isrequired to align the cavity 58 with the rod 18. To provide increasedflexibility in accommodating misaligned rods, axis 124 should beparallel to midline 30 when axis 126 is parallel to the slot 40 todefine a neutral angular position. In the neutral angular position, theattachment assembly 98 may rotate by approximately an equal amount ineither the clockwise or counterclockwise direction.

While the present invention has been illustrated by a description ofvarious preferred embodiments and while these embodiments have beendescribed in some detail, it is not the intention of the inventors torestrict or in any way limit the scope of the appended claims to suchdetail. Additional advantages and modifications will readily appear tothose skilled in the art. The various features of the invention may beused alone or in numerous combinations depending on the needs andpreferences of the user.

What is claimed is:
 1. An occipital plate, comprising: a base platehaving: an elongated central section with a midline; and a first sectionand a second section projecting laterally outward in opposite directionsfrom the midline of the base plate, wherein the first section comprisesa slot extending substantially parallel to a length of the firstsection; and an attachment assembly having: a slide member configured tomove along the slot of the first section; a post coupled to the slidemember, wherein the post has a first cross dimension and a second crossdimension wherein the first cross dimension of the post is less than afirst cross dimension of the slide member and wherein the second crossdimension of the post is approximately equal to a second cross dimensionof the slide member; and an angle limiting mechanism defining a range ofrotation of the attachment assembly, wherein a medial-lateral distancebetween the attachment assembly and the midline of the base plate isadjustable relative to the angle along the slot of the first section,wherein at least a portion of the attachment assembly is rotatable afterthe slide member is positioned in the slot and coupled to the baseplate, and wherein the angle limiting mechanism facilitates theattachment assembly to self-align or essentially self-align with a rodas the rod is received in an opening of the post of the attachmentassembly.
 2. The occipital plate of claim 1, wherein the second sectioncomprises a slot extending substantially parallel to a length of thesecond section, further comprising: a second attachment assembly havinga slide member constrained to move along the slot of the second section,wherein a medial-lateral distance between the second attachment assemblyand the midline of the base plate is adjustable relative to the anglealong the slot of the second section, and wherein at least a portion ofthe second attachment assembly is rotatable for angular orientation of asecond rod coupled thereto relative to the midline of the base plate. 3.The occipital plate of claim 1, wherein the first section furthercomprises: a terminating end opposite of the midline of the base plate;and an aperture at the terminating end for receiving a bone screwtherethrough.
 4. The occipital plate of claim 1, wherein the firstsection further comprises: a terminating end opposite of the midline ofthe base plate, wherein the terminating end is configured to allow theslide member of the attachment assembly to be positioned in the slot ofthe first section; and an end cap configured to be secured to theterminating end to retain the slide member of the attachment assembly inthe slot of the first section.
 5. The occipital plate of claim 1,wherein the slide member of the attachment assembly is elasticallydeformable for positioning in the slot of the first section.
 6. Theoccipital plate of claim 1, wherein the post is rotatable relative tothe slide member about an axis extending through the post and the slidemember.
 7. The occipital plate of claim 1, wherein the attachmentassembly further comprises a rivet, and wherein the post is coupled tothe slide member via the rivet.
 8. The occipital plate of claim 1,wherein the post is rigidly affixed to or integrally formed with theslide member.
 9. The occipital plate of claim 1, wherein geometry of theslide member of the attachment assembly allows the slide member torotate within the slot of the first section and relative to the baseplate.
 10. The occipital plate of claim 1, wherein the slide member isrotatable in the slot of the first section as permitted by the anglelimiting mechanism.
 11. The occipital plate of claim 10, wherein theangle limiting mechanism comprises at least one member projecting from aperiphery of the slide member for engagement with the slot of the basemember.
 12. The occipital plate of claim 10, wherein the angle limitingmechanism is part of the post, wherein the post is rigidly affixed to orintegrally formed with the slide member.
 13. The occipital plate ofclaim 1, wherein the slot of the first section comprises a groove,wherein the slide member of the attachment assembly comprises a flange,and wherein the groove of the slot and the flange of the slide membermate to limit movement of the slide member of the attachment assembly ina direction substantially perpendicular to the slot of the firstsection.
 14. The occipital plate of claim 1, wherein the angle is fixed.15. The occipital plate of claim 1, wherein the angle between the firstsection and the midline of the base plate is between approximately 10°and approximately 90°.
 16. The occipital plate of claim 15, wherein theangle between the first section and the midline of the base plate isbetween approximately 30° and approximately 70°.
 17. The occipital plateof claim 1, wherein the angle limiting mechanism comprises a pair oftriangularly-shaped wing members projecting from a periphery of theslide member.
 18. The occipital plate of claim 17, wherein each of thetriangularly-shaped wing members comprises bearing surfaces.
 19. Theoccipital plate of claim 18, wherein the bearing surfaces are angledwith respect to an axis by an angle B.
 20. The occipital plate of claim19, wherein the angle B controls an amount of rotation of the attachmentassembly.
 21. An occipital plate, comprising: a base plate having: anelongated central section with a midline; and a first section and asecond section projecting laterally outward in opposing directions fromthe midline of the base plate, wherein the first section comprises: aslot extending substantially parallel to a length of the first section;and a groove formed on side edges of the slot; and an attachmentassembly having: a slide member comprising at least one extensionprojecting from a periphery of the slide member to mate with the grooveformed on the side edges of the slot so that a dove-tail joint constructis formed between the base plate and the attachment assembly; and a postcoupled to the slide member, wherein the post has a first crossdimension and a second cross dimension, wherein the first crossdimension of the post is less than a first cross dimension of the slidemember, and wherein the second cross dimension of the post isapproximately equal to a second cross dimension of the slide member;wherein the slide member is constrained by the dove-tail joint constructto move along the slot of the first section, wherein a medial-lateraldistance between the attachment assembly and the midline of the baseplate is adjustable, wherein at least a portion of the attachmentassembly is rotatable after the slide member is positioned in the slotand coupled to the base plate, and wherein the at least one extension ofthe slide member is configured to limit angular orientation of a rodcoupled to the post of the attachment assembly to a range of anglesrelative to the midline of the base plate.